Easily manufactured exchange bias stabilization scheme

ABSTRACT

A problem associated with current bottom spin valve designs is that it is difficult to avoid magnetic charge accumulation at the edge of the sensor area, making a coherent spin rotation during sensing difficult to achieve. This problem has been eliminated by introducing an exchange coupling layer between the free layer and the ferromagnetic layer that is used to achieve longitudinal bias for stabilization and by extending the free layer well beyond the sensor area. After all layers have been deposited, the read gap is formed by etching down as far as this layer. Since it is not critical exactly how much of the biasing layers (antiferromagnetic as well as ferromagnetic) are removed, the etching requirements are greatly relaxed. Whatever material remains in the gap is then oxidized thereby providing a capping layer as well as a good interface for specular reflection in the sensor region.

This is a division of patent application Ser. No. 10/091,959 filing dateMar. 6, 2002, now U.S. Pat. No. 7,035,060, Easily Manufactured ExchangeBias Stabilization Scheme, which is herein incorporated by reference inits entirety.

FIELD OF THE INVENTION

The invention relates to the general field of read heads for magneticdisk systems with particular reference to bias stabilization.

BACKGROUND OF THE INVENTION

The principle governing the operation of the read sensor in a magneticdisk storage device is the change of resistivity of certain materials inthe presence of a magnetic field (MR or magneto-resistance).Magneto-resistance can be significantly increased by means of astructure known as a spin valve. The resulting increase (known as Giantmagneto-resistance or GMR) derives from the fact that electrons in amagnetized solid are subject to significantly less scattering by thelattice when their own magnetization vectors (due to spin) are parallel(as opposed to anti-parallel) to the direction of magnetization of thesolid as a whole

The key elements of what is termed a top spin valve are, starting at thelowest level, a seed layer, a free magnetic layer, a non-magnetic spacerlayer, a magnetically pinned layer, a pinning layer, and capping layer.When this order of layering is Inverted the resulting structure has thefree layer at the top and is termed a bottom spin valve. The presentinvention is concerned with the latter type. One advantage of this typeof design is that the capping layer, if made of certain materials, can,in addition to protecting the GMR stack from corrosion, also bring aboutmore specular reflection at the free layer-capping layer interface,thereby increasing the conductance. Isolation of the device fromextraneous magnetic fields is achieved by sandwiching it between twomagnetic shield layers.

Although the layers enumerated above are all that is needed to producethe GMR effect, additional problems remain. In particular, there arecertain noise effects associated with such a structure. As first shownby Barkhausen in 1919, magnetization in a layer can be irregular becauseof reversible breaking of magnetic domain walls, leading to thephenomenon of Barkhausen noise. The solution to this problem has been toprovide a device structure conducive to single-domain films for the GMRsensor and to ensure that the domain configuration remains unperturbedafter processing and fabrication steps and under normal operation. Thisis most commonly accomplished by giving the structure a permanentlongitudinal bias provided by two opposing permanent magnets.

Today, the most common sensor stabilization scheme uses a hard biasabutted junction structure as illustrated in FIG. 1. Seen there aresubstrate 11, seed layer 12, and layer 13 which represents anantiferromagnetic pinning layer as well as a pair of antiparallel pinnedlayers. Layer 16 is a copper spacer layer, layer 17 is the free layer,and layer 18 is a capping layer. The read element width is defined bythe edges that were milled out by etching. These edges are stabilizedthrough the magneto-static coupling provided by the adjacent hard biaslayer 14 which is separated from the sensor by non-magnetic seed layer12. This hard bias layer is traditionally similar to those magneticmedia materials which offer large coercivity, typically severalthousands Oesterds.

The major problem of this scheme is that it breaks the magneticcontinuity of the GMR sensor, and so cannot avoid magnetic chargeaccumulation at the edge of the sensor area, making a coherent spinrotation during sensing difficult to achieve without proper biasing.Traditional methods require a large magnetic moment to be put on theedge and utilize magnetostatic coupling to stabilize the edge spins. Asthe sensor size shrinks, these extra moments stiffen the whole sensorthus reducing sensor sensitivity to the media field. On the other hand,without these extra moments, transition through a multi-domain state isunavoidable during sensing. This could lead to higher noise level andreduce the sensitivity of the GMR sensor. This becomes more and moreserious as the sensor size reduces and the sensor edge region occupies alarger and larger proportion of the total GMR sensor area.

One simple alternative is to replace the hard bias layer with anexchange biased magnetic layer as shown in FIG. 2. Seen there is softmagnetic layer 24 which is permanently magnetized through exchangecoupling with antiferromagnetic (AFM) layer 25. Due to the abrupt cut ofthe junction edge in this scheme, it does not show a significantadvantage relative to the hard bias scheme. To ensure magneticcontinuity in the GMR sensor, it is preferred that the top magneticlayer not be touched during processing.

There are other schemes utilizing exchange bias to stabilize the GMRsensor edge. However, they all require extreme process control, like afew angstroms level etch control in order to be implemented. In thepresent invention we disclose a different approach, which provides acertain degree of specular reflection, a relatively large processwindow, a high exchange bias and convenience of integration into currentexisting process capabilities.

A routine search of the prior art was performed with the followingpublications of interest being found:

-   1. S. S. P. Parkin, “Systematic Variation of the Strength and    Oscillation Period of Indirect Magnetic Exchange Coupling through    the 3d, 4d, and 5d Transition Metals”, Phys. Rev. Lett., Vol. 67, P.    3598, 1991.-   2. B. Dieny, V. S. Speriosu, S. S. P. Parkin, B. A. Gurney, D. R.    Wilhoit and D. Mauri, “Giant Mangnetoresistance in soft    ferromagnetic multilayers”, Phys. Rev. B, Vol. 43, P. 1297, 1991.

The following patents were also encountered during our search.:

In U.S. Pat. No. 6,266,218, Carey et al. show a GMR with a Bottom SV andpatterned exchange process. U.S. Pat. No. 5,637,235 (Kim) discloses aBSV while U.S. Pat. No. 6,185,079 (Gill) shows an exchange biases DSV.U.S. Pat. No. 5,856,897 (Mauri) is a related GMR with AFM and FM layers.In U.S. Pat. No. 6,118,624, Fukuzawa et al. discuss abutted junctionsand in U.S. Pat. No. 6,313,973 Fuke et al. describe laminated exchangecoupling.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to establish exchange bias in the lead region of a bottom spinvalve without loss of GMR sensor sensitivity.

Another object of at least one embodiment of the present invention hasbeen to maintain specular reflection in said GMR sensor.

Still another object of at least one embodiment of the present inventionhas been to provide a process for manufacturing said bottom spin valve.

A further object of at least one embodiment of the present invention hasbeen that said process not require excessively tight etch control.

A still further object of at least one embodiment of the presentinvention has been that it be possible to deposit all layers involved insaid process during a single pumpdown.

These objects have been achieved by introducing an exchange couplinglayer between the free layer and ferromagnetic layer that is used toachieve longitudinal bias for stabilization. After all layers have beendeposited, the read gap is formed by etching down as far as this layer.Since it is not critical how much of the biasing layers(antiferromagnetic as well as ferromagnetic) are removed, the etchingrequirements are greatly relaxed. Whatever material remains in the gapis then oxidized thereby providing a capping layer as well as goodinterface in the sensor region for specular reflection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a bottom spin valve of the prior art including longitudinalhard bias.

FIG. 2 shows a bottom spin valve of the prior art including longitudinalexchange bias.

FIG. 3 illustrates an idealized approach to stabilizing the free layeroutside of the read gap.

FIG. 4 illustrates the structure of the present invention which is amanufacturable version of the structure seen in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the case of bottom spin valves, it would, in theory, be ideal if theAFM layer could be placed directly in contact with the free layer, withthe sensor region being left uncovered to sense the external mediafield. This idealized structure is illustrated in FIG. 3. Seen there (inaddition to features already shown in FIGS. 1 and 2) are pinning layer31, pinned layer 32 (actually a 3-layer laminate), non-magnetic spacer33, and free layer 34.

In practice, there are at least two problems associated with thisapproach. First, the GMR sensor as currently known to the art requires aspecial tantalum oxide capping layer to provide specular reflection atthe upper surface of the free layer. However, the presence of such acapping layer means that there cannot be any exchange bias. Limiting thecapping layer to the sensor region will require additional etch back toremove the exchange bias layer there or photo protection of the sensorregion, which can be extremely difficult to control when the sensor sizedrops down to a tenth of a micron. It is possible in principle to use alift-off process to avoid the extra etching step, but dimensionalcontrol and deposition over-spray become extremely difficult to controlin this case.

As shown in FIG. 4, the present invention solves this problem by firstintroducing an exchange coupling layer 41 between ferromagnetic layer 24and free layer 34. Additionally, layer 41 serves as an oxygen diffusionbarrier and spin filter, thereby increasing the GMR ratio. Read gap 43is then formed by selectively etching there all of layer 15 and at leastpart of layers 25 and 24, but not layer 41. A key novel feature of theinvention is that layer 42 is almost as effective as the currenttantalum oxide layer used by the art both as a protective layer and as apromoter of specular reflection at the upper surface of the free layer.This is confirmed in the data that is presented below in TABLE I:

TABLE I Layer 42 (pre- Layer 42 Rs dR oxidation) thickness (Å) ohms/sq.ohms dR/R tantalum 10 14.91 1.694 11.36 CoFe 25 14.68 1.649 11.23 whereRs is the sheet resistance and dR/R is the GMR ratio

Thus, substituting CoFe (which propagates exchange coupling) fortantalum (which does not) leaves the GMR ratio essentially unchanged.

To achieve good effective exchange coupling between layers 24 and 34 itis important to select the right materials for layer 41. Resultsobtained using several different layering combinations are summarized inTABLE II below:

TABLE II Layer 34 layer 41 layer 24 Hex Hc CoFe25 Cu5 CoFe25 142 43 Cu9156 17 Cu13 153 28 CoFe25 Ru9 CoFe25 173 13 Ru11 176 34 Ru13 186 44CoFe10/ Ru11 NiFe25 86 14 NiFe20 Ru13 83 18 CoFe10/ Ru10 CoFe45 120 20NiFe20 Ru7 Cu3 120 20 Ru5 Cu5 120 20 Ru3 Cu7 117 23 where Hex is theexchange bias and Hc is the coercivity of the laminate

These results demonstrate that there is a large selection of variousmaterials suitable for use in layer 41 (exchange coupling layer). It canthus be easily combined with GMR sensor considerations like high GMRratio, low current shunting, effective spin filtering, good corrosionresistance, and appropriate magnetostriction to achieve the best GMRperformance. Also, since the amount of layers 24 and 25 that getsremoved prior to oxidation is not critical, the process of the presentinvention provides a large etch-back window having a tolerance of tensof Angstroms instead of only a few Angstroms. This makes manufacturingprocess control significantly easier.

We now provide a detailed description of the process of the presentinvention. In the course of so doing, the structure of the presentinvention will also became apparent. Referring once more to FIG. 4, theprocess of the present invention begins with the deposition on asuitable substrate (not shown) of seed layer 12. This is followed by thesuccessive deposition of pinning layer 31, a pinned layer 32 (shown as a3-layer laminate), non-magnetic spacer layer 33 and free layer 34.

Next, as a key feature of the invention, exchange coupling layer 41 isdeposited. For the exchange coupling layer we have found any of thefollowing to be suitable: Cu, Rh, Ag, or Ru, with Ru being preferred.The thickness of layer 41 has been between about 3 and 20 Angstroms,with about 11 Angstroms being preferred. This is followed byferromagnetic layer 24, selected from among Fe, Co, and Ni, in anycombination, including added Ta, Cr, V, or W. Layer 24 could also be alaminate of two or more layers. Its thickness is between about 5 and 50Angstroms, with about 12 Angstroms being preferred.

Antiferromagnetic layer 25 is the next to be deposited. Any of NiMn,PtMn, IrMn, RhRuMn, CrMn, PtCrMn, PtinMn, FeMn, or NiFeMn could be used.Its thickness is between about 20 and 500 Angstroms (depending on whichmaterial is chosen), with about 40 Angstroms being preferred for thecase of Ru. Last to be deposited is conducting lead layer 15. This hasgenerally been gold but other materials such as Rh, Ni, Ag, Cu, Ti, orTa could also have been used. Its thickness is between about 50 and 500Angstroms.

Although it is optional to do so, all of these layers may be depositedduring a single pumpdown since no additional processing occurs until alllayers are in place. This offers obvious advantages with regard toconvenience and elimination of inter-layer contamination.

Patterning and etching the structure using standard photolithographictechniques now follows, the result of etching being to form opposingplugs whose separation defines the read width 43 of the structure. Asnoted above, all of layer 15 must be removed but the exact amount oflayers 24 and 25 that get removed is not critical, provided most oflayer 41 remains. With this approach, read gap widths between about 0.02and 0.3 microns are readily achieved.

Then, as another key feature of the invention, whatever remains oflayers 24 and 25 inside gap 43 is oxidized together with the part oflayer 41 that is present in the gap. Oxide layer 42 then serves tofacilitate specular reflection of conduction electrons at its interfacewith layer 41 and also acts as a protective layer for free layer 34. Theoxidation of layers 24 and 25 is achieved by user's choice of oxidationmethod including plasma oxidation, thermal oxidation, atomic oxidation,ion beam oxidation, and reactive ion oxidation.

The process ends with heating the structure in a magnetic field so as tofix the direction of magnetization in AFM layer 25 along a longitudinaldirection (corresponding to horizontal in FIG. 4). Heating is at atemperature of between about 150 and 300° C. for between about 10 and1,000 minutes in a magnetic field of between about 150 and 5,000 Oe (forthe case of IrMn).

1. A process for manufacturing a magnetic read head structure,comprising: providing a bottom spin valve structure having a topmostlayer that is a free layer having an upper surface; on said free layer,depositing an exchange coupling layer; on said exchange coupling layer,depositing a ferromagnetic layer; on said ferromagnetic layer,depositing an antiferromagnetic layer; on said antiferromagnetic layer,depositing a conducting lead layer; patterning and etching the structuredown to a depth that is sufficient to penetrate said antiferromagneticlayer, thereby forming a gap that defines a read width for thestructure; oxidizing all of said antiferromagnetic and ferromagneticlayers that are within said gap, thereby providing for specularreflection of conduction electrons at said free layer and exchangecoupling layer interface, providing an oxygen diffusion barrier,effecting improved spin filtering, and providing a protective layer forsaid free layer; and heating the structure in a magnetic field wherebysaid ferromagnetic layer becomes permanently biased in a longitudinaldirection by exchange coupling with said antiferromagnetic layer andsaid free layer outside of said gap becomes permanently biased in alongitudinal direction by exchange coupling with said ferromagneticlayer through said exchange coupling layer.
 2. The process described inclaim 1 wherein said exchange coupling layer is selected from the groupconsisting of Cu, Ru, Rh, and Ag, including being a laminate of morethan one member of said group.
 3. The process described in claim 1wherein said exchange coupling layer is deposited to a thickness betweenabout 8 and 20 Angstroms.
 4. The process described in claim 1 whereinsaid ferromagnetic layer is formed from any combination of elementsselected from the group consisting of Ni, Fe, Co, Al, Ta, Cr, V, and W.5. The process described in claim 1 wherein said ferromagnetic layer isdeposited to a thickness between about 5 and 50 Angstroms.
 6. Theprocess described in claim 1 wherein said antiferromagnetic layer isselected from the group consisting of NiMn, PtMn, IrMn, RhRuMn, CrMn,PtInMn, FeMn, and NiFeMn.
 7. The process described in claim 1 whereinsaid antiferromagnetic layer is deposited to a thickness between about20 and 500 Angstroms.
 8. The process described in claim 1 wherein saidconducting lead layer is any combination of elements selected from thegroup consisting of Au, Rh, Ni, Ag, Cu, Ti, and Ta.
 9. The processdescribed in claim 1 wherein said conducting lead layer is deposited toa thickness between about 50 and 500 Angstroms.
 10. The processdescribed in claim 1 wherein the step of oxidizing all of saidantiferromagnetic and ferromagnetic layers that are within said gapfurther comprises using a method selected from the group consisting ofplasma oxidation, thermal oxidation, atomic oxidation, ion beamoxidation, and reactive ion oxidation.
 11. The process described inclaim 1 wherein the step of heating the structure in a magnetic fieldfurther comprises heating at a temperature of between about 150 and 300°C. for between about 10 and 1,000 minutes in a magnetic field of betweenabout 250 and 5,000 Oe.
 12. A process for manufacturing a magnetic readhead structure, comprising: in succession with no intervening steps,depositing a seed layer, a pinning layer, a pinned layer, a non-magneticspacer layer, a free layer having an upper surface, an exchange couplinglayer, a ferromagnetic layer, an antiferromagnetic layer, and aconducting lead layer; patterning and etching the structure down to adepth that is sufficient to penetrate said antiferromagnetic layer toform a gap that defines a read width for the structure; oxidizing all ofsaid antiferromagnetic, ferromagnetic, and exchange coupling layers thatare within said gap, thereby providing for specular reflection ofconduction electrons at said free layer upper surface and providing aprotective layer for said free layer; and heating the structure in amagnetic field whereby said ferromagnetic layer becomes permanentlybiased in a longitudinal direction by exchange coupling with saidantiferromagnetic layer and said free layer outside of said gap becomespermanently biased in a longitudinal direction by exchange coupling withsaid ferromagnetic layer through said exchange coupling layer.
 13. Theprocess described in claim 12 wherein said exchange coupling layer isselected from the group consisting of Cu, Ru, Rh, and Ag, includingbeing a laminate of more than one member of said group.
 14. The processdescribed in claim 12 wherein said exchange coupling layer is depositedto a thickness between about 3 and 20 Angstroms.
 15. The processdescribed in claim 12 wherein said ferromagnetic layer is formed fromany combination of elements selected from the group consisting of Ni,Fe, Co, Al, Ta, Cr, V, and W.
 16. The process described in claim 12wherein said ferromagnetic layer is deposited to a thickness betweenabout 5 and 50 Angstroms.
 17. The process described in claim 12 whereinsaid antiferromagnetic layer is selected from the group consisting ofNiMn, PtMn, IrMn, RhRuMn, CrMn, PtInMn, FeMn, and NiFeMn.
 18. Theprocess described in claim 12 wherein said antiferromagnetic layer isdeposited to a thickness between about 20 and 500 Angstroms.
 19. Theprocess described in claim 12 wherein said conducting lead layer is anycombination of elements selected from the group consisting of Au, Rh,Ni, Ag, Cu, Ti, and Ta.
 20. The process described in claim 12 whereinsaid conducting lead layer is deposited to a thickness between about 50and 500 Angstroms.
 21. The process described in claim 12 wherein thestep of oxidizing all of said antiferromagnetic and ferromagnetic layersthat are within said gap further comprises using a method selected fromthe group consisting of plasma oxidation, thermal oxidation, atomicoxidation, ion beam oxidation, and reactive ion oxidation.
 22. Theprocess described in claim 12 wherein the step of heating the structurein a magnetic field further comprises heating at a temperature ofbetween about 150 and 300° C. for between about 10 and 1,000 minutes ina magnetic field of between about 250 and 5,000 Oe.